WO03/013444 discloses a one-part self-priming dental adhesive. WO03/013444 does not relate to dental adhesive compositions containing a polymerizable acidic phosphoric acid ester monomer.
Presently, self-etching, self-priming dental adhesives are composed of two-part systems due to low hydrolysis stability of conventional polymerizable acidic ester monomers. The low hydrolysis stability arises from the hydrolysis of acidic and adhesive monomers in water or water/solvent mixtures. Therefore, the known acidic and adhesive monomers must be stored water-free and mixed with the aqueous part just before application.
Frequently, sulfuric acids and phosphoric acid ester groups are employed in acidic polymerizable adhesive monomers. However, these acidic groups hydrolyze the acrylic and methacrylic ester moieties as well as the phosphoric acid ester groups within the monomers (Moszner et al. Macromol. Chem. Phys. 2000, 1062, (1999), DE 199 18 974, EP 1 169 996). In order to overcome these disadvantages, polymerizable phosphonic ester monomers were proposed by Moszner et al. (Macromol. Chem. Phys. 2000, 1062, (1999), DE 199 18 974, and EP 1 169 996). Moreover, U.S. Pat. No. 4,539,382 discloses mono(meth)acrylamides with one phosphonic acid group. However, these monomers still comprise hydrolysable(meth)acrylic ester moieties. Therefore, monomers with phosphonic acid ester groups based on 2-(oxa alkyl)acrylate were suggested in DE 197 46 708. However, also these phosphonic acid derivatives tend to hydrolyze in acidic solution. Therefore, it has not been possible to provide a one-part self-etching, self-priming dental adhesive composition. A one-part composition means that the composition is contained in only one container which may be stored. It allows application of the composition without any mixing and without any special equipment before the application. Self-etching means that the dental adhesive composition may be applied to a tooth without any preliminarily etching of enamel in a separate method step. In order to provide a self-etching feature, the composition must be acidic. Self-priming means that the dental adhesive composition may be applied to a tooth without any preliminarily application of a primer.
In practice the monomers of the prior art could be employed only in two-part dental systems which consist of a priming part and a bonding part. These two-part dental adhesive systems are either applied sequentially or in one step after mixing the two parts. Both procedures have inherent disadvantages due to clinical complications which might occur between sequential steps (saliva or blood contamination) or due to dosing problems when mixing is required prior to the application of the self-etching adhesive.
In order to overcome these clinical problems it is desired to provide a self-priming and self-etching adhesive as a one-part system eliminating the need of sequential application or premixing.
Further disadvantages of the monomers of the prior art containing phosphonic acid derivatives are as follows: The phosphonic acids are less acidic than phosphoric acid. Therefore, additional acids are required for obtaining the self-etching feature of a dental composition. However, the additional acid increases generally degradation of the monomer by hydrolysis. Moreover, the intermediates for producing the phosphonic acid derivatives are toxic. Therefore, the process for the preparation is dangerous and more complicated. Further, the phosphonic ester derivatives are more expensive than phosphoric acid derivatives.